RE: [RFC PATCH 00/56] Dynamic mitigations

Kaplan, David
2025-10-16T13:56:07Z

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Nicolas Bouchinet <nicolas.bouchinet@oss.cyber.gouv.fr>
> Sent: Thursday, October 16, 2025 8:55 AM
> To: Kaplan, David <David.Kaplan@amd.com>
> Cc: Josh Poimboeuf <jpoimboe@kernel.org>; Aaron Rainbolt
> <arraybolt3@gmail.com>; Thomas Gleixner <tglx@linutronix.de>; Borislav Petkov
> <bp@alien8.de>; Peter Zijlstra <peterz@infradead.org>; Pawan Gupta
> <pawan.kumar.gupta@linux.intel.com>; Ingo Molnar <mingo@redhat.com>; Dave
> Hansen <dave.hansen@linux.intel.com>; x86@kernel.org; H . Peter Anvin
> <hpa@zytor.com>; Alexander Graf <graf@amazon.com>; Boris Ostrovsky
> <boris.ostrovsky@oracle.com>; linux-kernel@vger.kernel.org; Xiujianfeng
> <xiujianfeng@huawei.com>; xiujianfeng@huaweicloud.com
> Subject: Re: [RFC PATCH 00/56] Dynamic mitigations
>
> Caution: This message originated from an External Source. Use proper caution
> when opening attachments, clicking links, or responding.
>
>
> [snip]
> > > LOCKDOWN_DEV_MEM is an integrity reason and should not be used for this
> > > scenario.
> > > I'd rather like to add a new Lockdown reason in the confidentiality set,
> > > maybe LOCKDOWN_CPU_MITIGATION ?
> > >
> >
> > Ok, that makes sense. Just to clarify, would that mean something like the below:
> >
> > diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> > index 3f9410dee67c..9b4864f84146 100644
> > --- a/drivers/base/cpu.c
> > +++ b/drivers/base/cpu.c
> > @@ -691,6 +691,9 @@ ssize_t cpu_write_mitigation_options(struct device *dev,
> > struct device_attribute *attr,
> > const char *buf, size_t count)
> > {
> > + if (security_locked_down(LOCKDOWN_CPU_MITIGATIONS))
> > + return -EPERM;
> > +
> > /* Save and filter the provided options. */
> > cpu_filter_mitigation_opts(buf);
> >
> > diff --git a/include/linux/security.h b/include/linux/security.h
> > index 92ac3f27b973..81cb52cf2111 100644
> > --- a/include/linux/security.h
> > +++ b/include/linux/security.h
> > @@ -153,6 +153,7 @@ enum lockdown_reason {
> > LOCKDOWN_TRACEFS,
> > LOCKDOWN_XMON_RW,
> > LOCKDOWN_XFRM_SECRET,
> > + LOCKDOWN_CPU_MITIGATIONS,
> > LOCKDOWN_CONFIDENTIALITY_MAX,
> > };
>
> You should also add an entry to the lockdown_reasons array in
> `security/security.c` with a description of the reason.
>

Ah right. Thanks!

--David Kaplan